media: smiapp: Set correct MODULE_LICENSE

The smiapp driver is licensed under GNU GPL v2 only, as stated by the
header. Reflect this in the MODULE_LICENSE macro.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>